Mixers are frequency translation devices that are widely used in communication, radar and electric warfare systems. Mixer performance depends on the power level and the frequency of the input and local oscillator signals. Because of the multiple degrees of freedom, mixers are difficult and time consuming to accurately characterize and model. The degrees of freedom include the power level and frequency of the input signal, radio frequency (RF) in down-converting application, or intermediate frequency (IF) in up-converting applications, and the local oscillator (LO) drive. Furthermore, the nonlinear devices inside the mixer circuits not only produce the desired translated signal, but also a multitude of harmonics and intermodulation products that make the modeling task increasingly difficult.
Generally, there are two ways to model mixers: circuit-level modeling and behavioral system modeling. Circuit-level modeling uses models for the internal components that comprise the mixer circuit. This must include accurate device models for the non-linear components used. Behavioral system modeling treats the mixer as a black box, using the external parameters of the mixer to describe its performance. This is of great importance, because often a system engineer has little circuit level information, yet requires accurate mixer system simulations. A variety of software packages are available to provide behavioral system mixer models. The models either depend upon polynomial functions or data files, such as intermodulation table (IMT) files to predict mixer performance. A conventional IMT file known in the art is a 2-dimensional table representing the relative amplitudes of the various frequency components, or spurs, appearing at the output of a mixer for a single specific set of input (fRF) and LO (fLO) frequency and power conditions according to the equation:fspur=|m×fRF±n×fLO|
Conventional IMT files used for mixer simulation store only the sum or difference intermodulation products under the assumption that the mixer is symmetrical, i.e. the corresponding sum and difference intermodulation products have the same amplitude. However, the assumption of symmetry does not always hold true. Current mixer modeling techniques known in the art do not address the multi-dimensional, dynamic and asymmetric nature of mixer output spectra.
Accordingly, what is needed in the art is an improved method for characterizing and modeling a device-under-test (DUT) over wide ranges of degrees of freedom. It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed.
However, in view of the prior art in at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.